Public water agencies that serve millions of residents in drought-weary California might only receive 10 percent of expected supplies in 2016 — half the amount that flowed to them this year through the state's massive system of reservoirs and canals, state officials say.

However, the early estimate could change, depending on the rain and snow that falls this winter, the state's Department of Water Resources said Tuesday.

Forecasters have said a strong El Nino weather system could drench California in the coming months. But one good winter might not be enough to rehydrate the parched state that has endured four bruising years of drought.

"Our historic drought has lasted for years and isn't going to quickly be washed away," said Mark Cowin, director of the Department of Water Resources.

The State Water Project supplies 29 public water agencies — from the San Francisco Bay Area to Southern California — that serve nearly two-thirds of California residents and irrigate nearly a million acres of farmland.

The drought has left California reservoirs at or near record low levels, and the water shortage has caused farmers to rely heavily on pumping groundwater.

Nearly all of the public water agencies that contract for State Water Project supplies have other sources, such as local reservoirs, streams and groundwater, to boost supplies, officials said.

This year, state water customers received 20 percent of their contracted amounts, and state officials say they hope the 2016 allocation will increase as rain and snow fall. But they also considered the possibility that drought could drag on another year.

Rich Atwater of the Southern California Water Committee said the drought underscores the need to update the state's water system. The committee represents business, government, agriculture and water agencies and works to inform Southern Californians about water.

"We need a modern water system that allows us to capture water when it's available so we can store enough water to protect us during the dry periods," Atwater said. "In the meantime, Californians must keep conserving."